Negative Sequence Cancellation in DFIGs via Independently Controlled Dynamic Braking Resistors

This paper extends the concept of using dynamic braking resistors (DBRs) in series with the stator of doubly-fed induction generators (DFIGs) to improve low-voltage ride-through (LVRT) performance, specifically under asymmetrical grid faults. Although previous studies have demonstrated the effectiveness of fixed or discrete-valued DBRs in mitigating electrical transients, mechanical issues such as torque loss remain mostly underexplored. In this work, we leverage independent control of the resistance in each stator phase by means of pulse-width modulation to maintain generator torque and cancel the negative sequence component of the grid voltage. By shaping the DBR voltage drop through asymmetric resistances, the resulting negative sequence voltage opposes that of the grid, reducing torque oscillations and enabling more stable DFIG operation during unbalanced faults. Analytical derivations and simulation results validate the proposed control strategy.